Free piston engine



A ril 7; 1964 H. KOSOFF 3,127,881

FREE PISTON ENGINE Filed Dec. 19, 1960 4 Sheets-Sheet l I N VEN TOR. Ham/a Kosqff April 7, 1964 H. KOSOFF FREE PISTON ENGINE 4 Sheets-Sheet 2 Filed Dec. 19, 1960 FIG.2

INVENTOR. I Ham/o (059/7 April 7, 1964 H. KOSOFF 3, 7,

FREE PISTON ENGINE Filed Dec. 19, 1960 4 Sheets-Sheet s FIG.4

INV EN TQR. Ham/0 (059 7 A ril 7, 1964 H. KOSOFF 3,127,881

FREE PISTON ENGINE Filed Dec. 19, 1960 4 Sheets-Sheet 4 FIG.5

INVENTOR. Ham/a Kosoff United States Patent f 3,127,331 FREE PlTON ENGINE Harold Kosoif, 1203 Hale St., fhiladeiphia 11, Pa. Filed Dec. 19, 1960, Ser. No. 76,933 33 Claims. (Cl. 123-46) This invention relates to an improvement on the free piston engine wherein mechanical devices hitherto required for synchronization of opposed pistons and for maintenance of proper limits on piston motion are elimi nated.

A free piston engine in its most basic form may be defined as a piston-cylinder device in which combustion products in one enclosed volume urges the piston to compress another enclosed volume, which in turn provides the energy to cause the piston to move inward to compress the fluid (gas) in the combustion chamber in preparation for the next combustion. The difference in energy required to compress the fluid (gas) in the combustion chamber and the energy released by expansion of the combustion products is available for useful work.

Commonly used mechanical devices for synchronizing opposed pistons cause friction and fluid losses, add to the size and weight of the engine, increase its complexity and decrease its reliability.

An object of this invention is to provide a free piston engine in which synchronization of pistons and/ or limitation of piston motion are achieved by a novel system of pneumatic control.

Another object of this invention is to maintain a predetermined compression ratio in the combustion chamber under diverse operating conditions.

A further object of this invention is to increase the engine flexibility by allowing the arrangement of an arbitrary number of piston-cylinder combinations around a common combustion chamber, common compressor chamber, or common rebounce device; or any combination thereof.

This invention relates to the entire class of internal combustion engines having one or more reciprocating pistons which in part define one or more common elastic volumes, and which are maintained in reciprocating motion by elastic forces. In brief, my invention consists of a system for controlling the average position of a piston (or pistons) of a free-piston engine by controlling the differential pressure acting on its faces. All embodiments of this invention maintain the compression ratio of the engine substantially constant despite changes in the load on the engine.

The invention is illustrated by the accompanying drawings of which FIGURE 1i is a diagram of forces in a free piston engine as shown. FIGURE lii is a diagram of forces on the center of mass of the engine shown in FIG- URE 11'. FIGURE 2 is a cross sectional view of a single piston free piston engine according to one form of my invention. FIGURE 3 is a cross sectional view of an arrangement of a single piston free-piston engine according to another form of my invention. FIGURE 4 is a cross sectional view of a two piston free-piston engine according to another form of my invention. FIGURE 5 is a cross sectional view of a three piston engine according to another form of my invention.

To explain this invention recourse is made to the following theorems from mechanics:

(I) The center of mass moves as if the total external force were acting on the entire mass of the system concentrated at the center of mass.

(II) If a mass is bound by elastic material and the kinetic energy over a finite period of time is not zero, the mass in fact will be oscillating.

Referring to FIGURE 1i, the respective centers of mass of the pistons 1, 2 may be replaced by point masses 3, 4.

3,127,881 Patented Apr. 7, 1964 Since piston 2 is further away from the point 0 than piston 1, the center of mass of the two pistons will be at point 5, i.e., to the right of axis y. The pistons are constrained to move along axes 6, 7, respectively. Point 0 is in the combustion chamber and at the intersection of axes 6, 7. The total external force F on the pistons 1 and 2 is where F is the sum of ,F and F the forces on the pistons exerted by the left and right rebounce chambers, respectively.

;F is the sum of F and fF the frictional forces at the piston-cylinder boundaries, left and right respectively.

F is the sum .of F and F the forces on the pistons exerted by the combustion chambers and compressor chambers, left and right respectively.

Axes 6 and 7 are equi-angular to axis x so that for equal displacements of the pistons from the point 0, equal components along h x axis will be produced. Axis y is the bisector of the included angle 6' between axis 6 of the left element and axis 7 of the right element. Axis x is perpendicular to axis y.

Refer to FIGURE lii. From Theorem I,

where Generally, R, will not equal 0 so that there will be an instantaneous velocity of the systems center of mass measured along x. Since P represents elastic forces the center of mass of the system will oscillate (Theorem 11) To synchronize the motion of the pistons it is necessary for R to be small otherwise the piston which is closer to center would strike the cylinder head at the end of the compression stroke. Analytically,

( x t xi'a x Where {E is the time average position .of the component of the systems center of mass along the x axis.

R is the instantaneous amplitude of the deviation of the systems center of mass from (R {R may be made to approach zero by varying F the average F. If $7,; is in the positive region, i.e., to the right of the y axis, selected ones of the variable forces F, F and P in Equation 1 are modified in accordance with this invention so that there is a change in T toward the negative region, i.e., toward the left of the y axis. And conversely, for [PI in the negative region, F is directed to the positive region. That is, we alter the pressure difference acting on each piston such that the net external force is changed in a direction to decrease {E Also, R must be small as stated above. In an engine :with two or more pistons the amplitude of oscillation of the center of mass must be much smaller than the amplitude of oscillation of the pistons, hence variations in F will be in phase with piston motion. By .design, the frequencies of oscillations of the center of mass and of the pistons are chosen so as to differ. Hence P will not be in phase with the oscillations of the center of mass and R will not build up to large values. Additionally, because of friction, R will approach zero.

For satisfactory operation the compression ratio must be maintained near a nominal value. This may be accomplished by varying F and {F}, the average rebounce forces acting on the left and right pistons, respectively. The compression ratio may be defined as the ratio of the total volume enclosed in the combustion chamber at the start of the compression stroke to the total volume enclosed therein at the end of that stroke. Assume that R is zero; if the compression ratio is larger than nominal, both ,F, and F must be reduced. This effectively causes a time average net force on each piston in the direction of lesser compression ratio. And conversely, for smaller than nominal compression ratio E and F are increased. This change in {F will increase the force on each piston in the direction of greater compression ratio. Since there are two forces which may be varied, the two engine parameters referred to above namely, (1) the position of the pistons center of mass and (2) the compression ratio may be controlled. The average position of the center of mass is controlled by the difference between F and F, and the compression ratio is controlled by the average The angle between the two elements (pistons) in FIGURE 1i may have any value. Since the proof may be applied to any two functionally connected elements without restriction, the number of elements, and the manner in which they are functionally connected are arbitrary, subject to geometric limitations and functional similarities.

For example, in FIG. 4 both the combustion chambers and the compressor chambers are connected and are common to both elements. Further, in FIG. 5 the rebouncecompressor chambers are connected and common to all elements as are the combustion chambers.

An engine of n elements must satisfy n conditions; n--1 conditions for small center of mass displacement, and 1 condition for nominal compression ratio. Thus, it degrees of freedom are required. For example, in a two piston engine the center of mass must be maintained near the y axis (Cf. FIG. 4); in a three piston engine the center of mass must be near the x and y axes (Cf. FIG. 5). To each element must be associated a variable independent force. In the given proof, the variable force was with the rebounce force. This is not a unique manner by which an independent variable force can be applied. The variable force may operate in either of two directions and may be with any existent force in an operative engine, be it the force of the combustion chamber, compression chamber, or rebounce chamber; or may be caused by a special chamber included for that purpose.

FIGURE 2 shows a simple embodiment of a freepiston engine having a single piston 1, a combustion chamber 0 bounded by a cylinder head 11 and the upper face 12 of the piston, a fuel injector illustrated schematically at the numeral 13, an exhaust port 14 and an intake port 15. There is also a compresison chamber 16 which is bound by a cylinder wall 17 and a middle cylinder head 18. The enlarged diameter portion of the piston has an annular piston face 19 and an opposed piston end face 24. The cylinder head portion 18 includes a suction port 20 having an associated valve which opens on the power stroke and which closes during the compression stroke. It also includes port 21 with an associated valve which opens on the compression stroke and closes on the power stroke. There is an axial passageway in piston 1 which begins at the center of the face 24. A vent pipe 28 passes through this passageway, there being a vent 29 located near the inner end of the pipe. Below the face 24 is the rebounce chamber 22 which is bounded by the cylindrical wall 17 and the lower end wall 23. The end wall 23 is provided with a very small orifice 26 to which is connected a conduit 27 leading from a source 31 of a fluid such as air. This source may be an accumulator, a pump, or a coupling to another part of the engine which develops fluid under pressure. The pressure within source 31 must be greater than the pressure in the rebounce chamber. There must be a pressure drop across the small orifice 26. The vent pipe passes through a centrally located aperture in the end wall 23 and is connected to a fluid receiver 30.

The pressure responsive fuel injector 13 is connected to the compression or pump chamber 16 by conduit 25, and is activated by the pressure changes in the said chambers. The construction and operation of the fuel injector 13 is not part of the present invention and is presented merely to illustrate a typical environment for the engine. Reference is made, in this connection, to US. Patent 2,425,850 to R. I. Welsh and to FIG. 5 thereof.

As there is only one piston, there is no synchronization control. My invention is useful with a single piston engine since it will maintain the compression ratio essentially constant. In brief, control of the compression ratio is accomplished by adjusting the axial pressure differential operative on the piston. It does this in the case of the embodiment shown in FIG. 2 by varying the pressure in the rebounce chamber 22 as a function of the length of the pistons compression stroke. If the piston moves excessively inward (greater than nominal compression ratio) relatively more of the area of the vent 29 is uncovered so that the pressure built up in the chamber 22 (by gas leaking into chamber 22 from source 31) is lowered by the escape of greater amounts of gas through conduit 28 'to the receiver 30. Thus, during the following cycles the pressure differential on the piston will increase in the outward direction so that the piston will not tend to travel so far inward.

If, on the contrary, the piston is travelling less than a predetermined inward distance so that the compression ratio is less than a predetermined nominal value, less of the area of the vent 29 will be exposed at the end of the compression stroke. Hence, less gas will flow out of chamber 22 and the pressure will increase therein, because of the continuous flow of gas from the source 31. This pressure will continue to rise and the piston will move more inwardly on its compresison stroke. When the desired compression ratio is attained, there will be no net flow of gas through the chamber 22. No net flow means that the mass of gas flowing into the rebounce chamber via small orifice 26 during a cycle equals the flow out via vent 29 when the piston is near its most inward position. In actuality, within one cycle the net flow would not be exactly zero, but rather, would, over many cycles, remain very close to zero and the predetermined nominal compression ratio would be very closely attained.

It is possible to change the nominal compression ratio by changing the size of the small orifice 26, the area of the vent 29, the position of the vent 29, the pressure in the source 31, or the pressure in the receiver 30.

The engine pictured in FIG. 2 is presented in a simplified version as it is not necessary for purposes of explaining this invention to show some of the conventional parts of a free-piston engine such as the source of compressed air normally used for scavenging the combustion chamber. Also, the fluid source and receiver could be integrated into the engine itself.

FIGURE 3 shows a variant of FIGURE 2 which,

instead of being operative on the pressure in the rebounce chamber to influence the net pressure axially of the piston, works by adjusting the pressure in a chamber bounded partially by the upper annular face of the piston. Compressor chamber 40 is opposite the combustion chamber 0 and functions as the rebounce chamber. Conduit 41 communicates the pressure responsive fuel injector 13 with the control chamber 42. Control chamber maintains a variable force. Since the direction of the varia le force is opposite to the direction as illustrated in 5 FIGURE 2, the previously described mechanism for varying the variable force is reversed. A small orifice 43 communicates the control chamber 42 with a fluid receiver 44 via conduit 45. Piston motion on the compresison stroke beyond a predetermined point communicates the control chamber with a fluid source 49 via exposed vent 46 and conduit 47, and conduit 48 which is defined by and within said piston. It is understood that in the structure of FIG. 3, there is provided means (not shown) for insuring that the rear end of the conduit 48 can communicate with the conduit 47 if the inward stroke of the piston exceeds a certain minimum distance. This may be accomplished by insuring that there is no rotation of the piston about its axis which may be accomplished, for example, by forming a longitudinal ridge on the inner wall of the rebounce chamber which mates with a corresponding groove in the outer surface of the large diameter part of the piston, the groove being par- ;allel to the axis of the piston. Alternatively, provision can be made for supplying pressurized air via the rear opening of the conduit 48 despite rotation of the piston. Thus, there could be many of the vents 46 formed in a circular row around the cylinder, all of the them being connected to one or more sources of pressurized gas.

Another way of accomplishing the same result is by having just one vent 46 as shown but providing a circular groove formed in the periphery of the larger diameter portion of the piston. The groove is located to communicate with the rear opening of the conduit 48 so that even if the piston rotates, compressed air will be applied via the groove to the conduit 48 and thence to the control chamber 42.

Vent 46 is so positioned that it is not normally exposed at the end of the combustion stroke of the piston. If it were, pressurized gas from source 49 would flow into the control chamber 42 thereby exacerbating the condition which is to be counteracted.

When the compression ratio is less than nominal, the passageway 48 will be in communication with a lesser area of the opening 46 with the result that there will be a net outflow of fluid from chamber 42 into receiver 44, thereby decreasing the pressure therein. This decreased pressure in control chamber 42 allows greater inward travel of the piston with a resultant greater compression ratio.

When the compression ratio exceeds the nominal value, a greater amount of gas will enter 42 from 49, hence there will be a net gain of fiuid and pressure increase in the control chamber 42. This increase of pressure acting downward will decrease the length of the inward stroke and thereby lower the compression ratio.

FIGURE 4 shows a common form of the free piston engine. This may be constructed by joining two elements, as defined in FIGURE 2, at their combustion chamber cylinder heads, and by joining the two elements at the compressor chamber via conduit 50. An exhaust port 51 and intake port 52 are placed at opposite ends of the combustion chamber 0. Conduit 53 communicates the pressure responsive fuel injector 13 with the compressor chamber 5.4 and 55.

In order to maintain the compression ratio of the engine substantially constant and to synchronize the strokes of the respective pistons, I provide for adjustment of the pressure in the rebounce chambers 58 and 59 as a function of the average positions of the pistons. This is accomplished by providing a source of fluid at a higher pressure than ordinarily exists in the rebounce chambers. This source is the chamber 60 which provides gas to scavenge the combustion chamber through port 52 and communicates with the compression chambers 54 and 55 by valves which open on the in-stroke of the pistons. The chamber 60 is coupled through an aperture in the cylinder wall to conduits 63 and 64 which are respectively connected to small orifices 56 and 57 in the opposing end walls of the cylinder. In addition, to provide for outflow of the fluid in the rebounce chambers, there are provided vents 61 and 62 in the cylinder wall. The pressure in the rebounce chambers is adjusted and the vents 61 and 62 are so positioned that when the pistons have the desired nominal compression strokes, the time average flow of fluid through the rebounce chambers at this steady state condition is zero. If the pistons travel inwardly a distance which is more than a predetermined nominal distance more of the area of the vents 61 and 62 will be uncovered and the pressure in the chambers 58 and 59 will be decreased by the consequent greater outflow of the fluid through the vents 61 and 62. As a result, the pressure differential on the opposed faces of each piston will increase to produce a net outward force so that the inward stroke of the piston will be decreased. Conversely, if the pistons do not travel sufficiently inward, with respect to a predetermined nominal distance, less of the fluid will escape through the vent, than enters through small orifices 56 and 57. Thus, the pressure will begin to increase in the chambers 58 and 59 so as to impel the pistons more inwardly.

The preceding discussion described the mechanism by which the compression ratio is maintained near constant. In brief, the pressure in the rebounce chamber is adjusted as a function of the pistons inward stroke, i.e., the compression ratio. The same mechanism also maintains piston synchronization. At steady state conditions the time average net flow through each rebounce chamber, because of this mechanism, is zero. Since the fluid into each rebounce chamber 58 and 59 is set near equal by adjustment of the size of the small orifice (the small orifice may be a needle valve) and the time average net flow is zero, the time average fluid outflow through vents 61 and 62 is near equal. This means that each vent 61 and 62 is open for approximately the same duration. By design, the frequency of oscillation of the center of mass differs from the frequency of oscillation of the pistons. This means that at the time of vent opening, occurring once each cycle of piston oscillation when the pistons are near their most inward position, the center of mass may be at any position in its oscillation. If the center of mass at the time of vent opening is left of center, the right vent will be opened more; and if the center of mass at the time of vent opening is right of center, the left vent will be opened more. Since over a long period of time each vent is opened for about the same duration, the average position of the center of mass is neither to the left or right, but rather near the center. Referring to the earlier discussion, we find that the maintenance of the time average position of the center of mass, fi near the engine center satisfies the condition necessary for synchronization.

As described earlier, the difference in pressure between the rebounce chambers 58 and 5-9 controls the position of the center of mass, and the magnitude of the average pressure controls the compression ratio.

Thus, a natural consequence of the maintenance of nominal compression ratio is the maintenance of synchronized piston motion. In this illustration the rebounce force and variable force are the same.

FIGURE 5 shows an arrangement whereby 3 free piston engines as defined by FIGURE 3 are joined at their combustion chamber cylinder head. As in the structure shown in FIG. 3, means may be provided either for preventing rotation of the piston or for insuring that pressurized gas is applied to the rear opening of the conduits through the pistons despite rotation of the pistons. The three combination compressor-rebounce chambers 70, 71, 72 communicate via conduit 73. The control chambers 74, 75, 76 each are the means by which the three variable forces are applied. Through these control chambers fluid pressure from the sources 84, and 86 is applied through respective vents 81, 82 and 83. Each of the pistons has a longitudinal passageway which enables the vents to communicate with the corresponding ones of the control chambers.

Each control chamber 74, 75, 76 contains a small orifice 78, 79, 80, respectively, which communicates the control chamber with a fluid receiver (in this example, the atmosphere), and a vent 81, 82, 83 which communicates the corresponding control chamber with a fluid source 84, 85, 86, respectively, in the event of greater than nominal inward piston motion in that control chamber. If there is a greater than a predetermined nominal inward movement of the piston, the passageways in the pistons enable the pressure from the source 84 to be built up in the control chambers thereby tending to diminish the length of the inward stroke. As in the previous examples, if the inward stroke is smaller than the predetermined nominal length, pressure is diminished in the control chambers.

Illustrated are one intake port 99 and two exhaust ports 91, 92. Means for charging the combustion chamber are not shown.

The term cylinder is not limited to surfaces generated by rotating a straight line about a parallel axis. Such diverse surfaces as may be generated by rotating, by 2 pi or less, an arbitrary curve about an axis are included by the term cylinder. For example, a toroid or sphere may be satisfactorily used as a cylinder.

It is to be understood that the invention is not limited to a specific embodiment herein illustrated and described, but may be used in other ways without departing from the spirit as defined in the following claims.

What I claim as my invention and desire to secure by Letters Patent is:

1. A free piston engine comprising:

(a) at least one cylinder,

(b) at least one free piston each of which has a plurality of faces, at least portions of said faces opposing one another, each of said pistons being arranged to move axially in a reciprocating fashion in a corresponding one of said cylinders, and

(c) means including a source of gas under pressure for supplying said pressurized gas to at least one chamber bounded by a face portion of one piston and said cylinder thereby controlling the average positions of said pistons, said means being arranged to vary the gaseous pressure exerted axially upon said pistons in response to deviations of the respective average positions thereof from predetermined average positions.

2. The engine according to claim 1 wherein said means also includes means associated with said cylinders for receiving said gas.

3. The engine according to claim 2 wherein said receiving means includes apertures formed in said cylinders.

4. The engine according to claim 3 wherein said (0) means also includes apertures formed in said cylinders whereby gas from said source can enter said cylinders.

5. A free piston engine comprising:

(a) a cylinder,

(b) a plurality of free pistons arranged for reciprocal axial movement within said cylinder, each having opposing face portions,

(0) means for continuously applying varying amounts of gas under pressure to the rebounce chambers for the respective pistons, said chambers respectively being bounded in part by the outer faces of said pistons, and

(d) means associated with the wall of said cylinder for releasing said pressurized gas from said chambers as a function of the extent of the inner stroke of said pistons to regulate the differential axial pressure on said respective pistons.

6. The engine according to claim 5 wherein said gasreleasing means includes vents in the walls of said cylinder arranged substantially transverse to the direction of movement of said pistons and wherein said gas-applying 8 means includes a source of gas under pressure connected to said rebounce chambers through small orifices in the end walls of said cylinder.

7. The invention according to claim 6 wherein said source of gas is an auxiliary chamber in said cylinder into which said gas is compressed by the action of said pistons in the compression chambers respectively associated therewith, said compression chambers communicating with said auxiliary chamber by passageways equipped with outlet valves.

8. In an internal combustion engine of the free piston type, the combination comprising, a power cylinder, a power piston adapted to reciprocate within said power cylinder, a compressor chamber defined in part by extensions of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston for compressing elastic material within said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving the power piston on the compression stroke; means operatively associated with said power piston for increasing a force acting on said power piston in the direction of greater combustion chamber expansion if said power piston on the compression stroke passes a specified point, and means operatively associated with said power piston for decreasing a force acting on said power piston in the direction of greater combustion chamber expansion if said power piston on the compression stroke does not pass a specified point.

9. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 8, wherein to the rebounce device of each element is operatively joined to the rebounce of other elements such that all elements have a rebounce device in common.

10. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 8, wherein all elements are operatively joined at the compressor chamber such that all elements have a compressor chamber in common.

11. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 8, wherein all elements are operatively joined at the combustion chamber such that all elements have a combustion chamber in common, and further, all elements are operatively joined at the compressor chamber such that all elements have a compressor chamber in common.

12. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 8, wherein all elements are operatively joined at the combustion chamber such that all elements have a combustion chamber in common, and further, all elements are operatively joined at the rebounce device such that all elements have a rebounce device in common.

13. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 8, wherein each element is operatively joined with at least one other element such that each element has in common with at least one other element functional parts of an element.

14. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements each of which contains a power cylinder, a power piston adapted to reciprocate within said power cylinder, a compressor chamber defined in part by extensions of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston for compressing elastic material of said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving the power piston on the compression stroke; first non-mechanical means operatively associated with said power piston for increasing a force acting on said power piston in the direction of greater combustion chamber compression if said power piston on the compression stroke does not pass a specified point, said first non-mechanical means including pressure-drop producing means, and first non-mechanical means operatively associated with said power piston for decreasing a force acting on said power piston in the direction of greater combustion chamber compression if said power piston on the compression stroke does pass a specified point.

. 15. In an internal combustion engine of the free piston type as defined in claim 14, wherein each element is operatively coupled to the other at the compressor chamber such that all elements efiectively have a compressor chamber in common.

16. In an internal combustion engine of the free piston type as defined in claim 14, wherein each element is operatively coupled to the other at the combustion chamber such that all elements effectively have a combustion chamber in common, and further, each element is operatively coupled to one another at the compressor chamber such that all elements effectively have a compressor chamber in common.

17. In an internal combustion engine of the free piston type as defined in claim 14, wherein each element is operatively coupled to the other at the combustion chamber such that all elements effectively have a combustion chamber in common, and further, each element is operatively coupled to the other at the rebounce device such that all elements effectively have a rebounce device in common.

18. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements each of which contains a power cylinder, a power piston adapted to reciprocate within said power cylinder, a compressor chamber defined in part by extensions of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston for compressing elastic material within said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving the power piston on the compression stroke; means operatively associated with said power piston for increasing a force acting on said power piston in the direction of greater combustion chamber expansion if said power piston on the compression stroke passes a specified point, and means operatively associated with said power piston for decreasing a force acting on said power piston in the direction of greater combustion chamber expansion if said power piston on the compression stroke does not pass a specified point.

19. In an internal combustion engine of the free piston type, the combination comprising a power cylinder, a power piston adapted to reciprocate Within said power cylinder, a compressor chamber defined by a first extension of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston for compressing elastic material of said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving said power piston on the compression stroke; said power piston having operative means whereby fluid pressure acting on a second extension of said power piston positioned within a second extension of said power cylinder and acting in a direction of greater combustion chamber compression, be increased by means of a small orifice which maintains communication between the second extension of the power cylinder and a fluid source, and further, a vent so positioned that if said power piston on the compression stroke does pass a specified point, the pressure be decreased by virtue of the consequent communication between said second extension of said power cylinder and a fluid receiver.

20. In an internal combustion engine of the free piston type, the combination comprising a power cylinder, a power piston adapted to reciprocate within said power cylinder, a compressor chamber defined by a first extension of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston'for compressing elastic material within said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving said power piston on the compression stroke; said power piston having operative means whereby fluid pressure acting on a second extension of said power piston positioned within a second extension of said power cylinder and acting in a direction of greater combustion chamber expansion, is decreased by means of a small orifice which maintains communication between the second extension of the power cylinder and a fluid receiver, and further, a vent so positioned that if power piston on the compression stroke does pass a specified point, the pressure is increased by virtue of the consequent communication between the second extension of said power cylinder and a fluid source.

21. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 20, wherein all elements are operatively joined at the rebounce device such that all elements have a rebounce device in common.

22. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 20, wherein all elements are operatively joined at the compressor chamber such that all elements have a compressor chamber in common.

23. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 20, wherein all elements are operatively joined at the combustion chamber such that all elements have a combustion chamber in common, and further, all elements are operatively joined at the compressor chamber such that all elements have a compressor chamber in common.

24. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 20, wherein all elements are operatively joined at the combustion chamber such that all elements have a combustion chamber in common, and further, all elements are operatively joined at the rebounce device such that all elements have a rebounce device in common.

25. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements as defined in claim 20, wherein all elements are operatively joined with at least one other element such that each element has in common with at least one other element functional parts within an element.

26. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements each of which contains a power cylinder, a power piston adapted to reciprocate within said power cylinder, a compressor chamber defined by a first extension of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston for compressing elastic material of said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving the power piston on the compression stroke; said power piston having operative means whereby fluid pressure acting on a second extension of said power piston positioned within a second extension of said power cylinder and acting in a direction of greater combustion chamber compression, be increased by means of a small orifice which maintains communication between the second extension of said power cylinder and a fluid source, and further, a vent so positioned that if said power piston on the compression stroke does pass a specified point, the pressure be decreased by virtue of the consequent communication between said second extension of said power cylinder and a fluid receiver, wherein each element be operatively joined at the combustion chamber such that all elements have a combustion chamber in common.

27. In an internal combustion engine of the free piston type as defined in claim 26, wherein each element is operatively coupled to the other at the rebounce device such that all elements efiectively have a rebounce device in common.

28. In an internal combustion engine of the free piston type as defined in claim 26, wherein each element is operatively coupled to the other at the compressor chamber such that all elements effectively have a compressor chamber in common.

29. In an internal combustion engine of the free piston type as defined in claim 26, wherein each element is operatively coupled to the other at the combustion chamber such that all elements effectively have a combustion chamber in common, and further, each element is operatively coupled to the other at the compressor chamber such that all elements efiectively have a compressor chamber in common.

30. In an internal combustion engine of the free piston type as defined in claim 26, wherein each element is operatively coupled to the other at the combustion chamber such that all elements effectively have a combustion chamber in common, and further, each element is operatively coupled to the other at the rebounce device such that all elements efifectively have a rebounce device in common.

31. In an internal combustion engine of the free piston type, the combination comprising a plurality of elements each of which contains a power cylinder, a power piston adapted to reciprocate within said power cylinder, a compressor chamber defined by a first extension of said power piston and said power cylinder, a rebounce device, means operatively associated with said power piston for compressing elastic material within said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving the power piston on the compression stroke; said power piston having operative means whereby fluid pressure acting on a second extension of said power piston positioned within a second extension of said power cylinder and acting in a direction of greater combustion chamber expansion, is decreased by means of a small orifice which maintains communication between the second extension of the power cylinder and a fluid receiver, and further, a vent so positioned that if said power piston on the compression stroke does pass a specified point, the pressure is increased by virtue of the consequent communication between the second extension of said power cylinder and a fluid source, wherein all elements are operatively joined at the combustion chamber such that all elements have a combustion chamber in common.

32. In an internal combustion engine of the free piston type, the combination comprising a power cylinder, a power piston adapted to reciprocate within said power cylinder a rebounce device, means operatively associated with said power piston for compressing elastic material within said rebounce device on the combustion stroke of said power piston, the energy in said compressed elastic material driving the power piston on the compression stroke; means substantially continuously operative during operation of said engine for controlling the average position of said pistons, said controlling means being responsive to the location of the terminal point of said power piston travel at the end of its compression stroke and start of its combustion stroke, said control means also including a pressure-drop producing means, said control means operatively connected to said power piston for varying a force acting axially on said power piston in response to the displacement of said terminal point from a specified point.

33. In an internal combustion engine of the free piston type, the combination comprising a housing having a cylinder formed therein, a piston adapted to reciprocate within said cylinder, a combustion chamber at one end of said cylinder, rebounce means at the other end of the cylinder operatively connected to one face of said piston for driving the piston in the compression stroke, the means operative substantially continuously during operation of said engine for controlling the average position of said piston, said controlling means being responsive to the location of the terminal point of piston travel at the end or" its compression stroke and start of combustion stroke operatively connected to said piston for varying the pneumatic force acting axially on said piston said control means also including a pressure-drop producing means.

References Cited in the file of this patent UNITED STATES PATENTS 1,089,892 Zoelly Mar. 10, 1914 1,858,102 McKeown May 10, 1932 2,025,177 Pescora Dec. 24, 1935 2,083,680 Anderson et al. June 115, 1937 2,406,037 Ramsey Aug. 20, 1946 2,434,280 Morain Jan. 15, 1948 2,434,778 Welsh Jan. 20, 1948 2,666,569 Bent Jan. 19, 1954 2,815,641 Ramsey et al. Dec. 10, 1957 2,849,995 Lewis Sept. 2, 1958 2,916,025 Klatsch Dec. 8, 1959 2,955,580 MacDonald Oct. 11, 1960 FOREIGN PATENTS 814,540 Germany Jan. 24, 1952 

1. A FREE PISTON ENGINE COMPRISING: (A) AT LEAST ONE CYLINDER, (B) AT LEAST ONE FREE PISTON EACH OF WHICH HAS A PLURALITY OF FACES, AT LEAST PORTIONS OF SAID FACES OPPOSING ONE ANOTHER, EACH OF SAID PISTON BEING ARRANGED TO MOVE AXIALLY IN A RECIPROCATING FASHION IN A CORRESPONDING ONE OF SAID CYLINDERS, AND (C) MEANS INCLUDING A SOURCE OF GAS UNDER PRESSURE FOR SUPPLYING SAID PRESSURIZED GAS TO AT LEAST ONE CHAMBER BOUNDED BY A FACE PORTION OF ONE PISTON AND SAID CYLINDER THEREBY CONTROLLING THE AVERAGE POSITIONS OF SAID PISTONS, SAID MEANS BEING ARRANGED TO VARY THE GASEOUS PRESSURE EXERTED AXIALLY UPON SAID PISTONS IN RESPONSE TO DEVIATIONS OF THE RESPECTIVE AVERAGE POSITIONS THEREOF FROM PREDETERMINED AVERAGE POSITIONS. 